<abstract xmlns="http://www.w3.org/1999/xhtml">

<p>The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a microorganism that causes coronavirus disease 2019 (COVID-19). Mutations affect evolutionary conservation of microorganisms. The fast pace evolutionary changes are currently affecting pathogenicity of SARS-CoV-2. In this study, the structural fluctuations of the amino acid residues in the spike glycoprotein and RNA-dependent RNA polymerase (nsp12) of SARS-CoV-2 were investigated by in silico approach using structural flexibility dynamics to decipher susceptibility to mutation. The result of this study implicated key amino acid residues (with rmsf) which could be very susceptible to mutation, which include residues 50 (3.79 Å), 119 (4.56 Å), 120 (3.53 Å), 220 (3.84 Å), 265 (4.31 Å) of RNA-dependent RNA polymerase (nsp12), as well as residues 477 (4.21 Å), 478 (4.82 Å), 479 (5.40 Å), 481 (5.94 Å), 560 (4.63 Å), 704 (4.02 Å), 848 (4.58 Å), 1144 (4.56 Å) and 1147 (4.61 Å) of spike glycoprotein. The SARS-CoV-2 mutations destabilized the overall protein structure in multiples of amino acid residues which could interfere with active site leading to insensitivity or resistance to the inhibitors. Mutation T478K of Spike glycoprotein showed the highest deviation in the structure. Overall, spike glycoprotein has the highest number of mutations, and these variants could increase the risk to human health if not mitigated in the population.</p>
</abstract>

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a microorganism that causes coronavirus disease 2019 (COVID-19). Mutations affect evolutionary conservation of microorganisms. The fast pace evolutionary changes are currently affecting pathogenicity of SARS-CoV-2. In this study, the structural fluctuations of the amino acid residues in the spike glycoprotein and RNA-dependent RNA polymerase (nsp12) of SARS-CoV-2 were investigated by in silico approach using structural flexibility dynamics to decipher susceptibility to mutation. The result of this study implicated key amino acid residues (with rmsf) which could be very susceptible to mutation, which include residues 50 (3.79 Å), 119 (4.56 Å), 120 (3.53 Å), 220 (3.84 Å), 265 (4.31 Å) of RNA-dependent RNA polymerase (nsp12), as well as residues 477 (4.21 Å), 478 (4.82 Å), 479 (5.40 Å), 481 (5.94 Å), 560 (4.63 Å), 704 (4.02 Å), 848 (4.58 Å), 1144 (4.56 Å) and 1147 (4.61 Å) of spike glycoprotein. The SARS-CoV-2 mutations destabilized the overall protein structure in multiples of amino acid residues which could interfere with active site leading to insensitivity or resistance to the inhibitors. Mutation T478K of Spike glycoprotein showed the highest deviation in the structure. Overall, spike glycoprotein has the highest number of mutations, and these variants could increase the risk to human health if not mitigated in the population.


<div xmlns="http://www.w3.org/1999/xhtml">
<sec id="j_acb-2021-0020_s_001"><div>Introduction</div>
<p>The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a pathogen that causes coronavirus disease 2019 (COVID-19) which was first recorded at Wuhan city, China in December 2019, and it has caused 262,866,050 confirmed cases which has resulted to over 5,224,519 deaths worldwide as of 3 December 2021 [<a ref-type="bibr" href="#j_acb-2021-0020_ref_001">1</a>]. Mutations affect evolutionary conservation of microorganisms. The emergence of new variants is an expected occurrence as it has been the case of SARS-CoV-2. A variation of SARS-CoV-2 due to evolution and adaptation processes has been detected globally. While most emerging mutations will not have significant impact on the spread of the virus, some mutations or combinations of mutations may provide the virus with a selective advantage, such as increased transmissibility or the ability to evade the host immune response. In that instances, the variants could increase the risk to human health and are considered to be variants of concern (VOC) [<a ref-type="bibr" href="#j_acb-2021-0020_ref_002">2</a>].</p>
<p>Since the outbreak of COVID-19 pandemic, new SARS-CoV-2 variants have been reported from the United Kingdom, France, South Africa, Denmark, and Nigeria [<a ref-type="bibr" href="#j_acb-2021-0020_ref_002">2</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_003">3</a>]. The fast pace evolutionary changes are currently affecting pathogenicity of SARS-CoV-2 as the third-wave slams the global communities, and this called for urgent <italic>in silico</italic>, <italic>in vitro</italic>, and <italic>in vivo</italic> studies [<a ref-type="bibr" href="#j_acb-2021-0020_ref_004">4</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_005">5</a>]. According to Huang et al. [<a ref-type="bibr" href="#j_acb-2021-0020_ref_006">6</a>], SARS-CoV-2 protein mutations have two imperative features: (i) a higher ability to infect and enhanced pathogenicity than the bat-like SARS-CoV, and (ii) a lower pathogenicity than SARS-CoV. It has been reported that the existing approved vaccines which include two mRNA-based anti-SARS-CoV-2 vaccines; BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna), as well as three inactivated virus-based vaccines; BBIBP-CorV vaccine (Sinopharm), BBV152 (Bharat Biotech International Limited), and CoronaVac (Sinovac Biotech), were significantly less protective against Beta variant of coronavirus [<a ref-type="bibr" href="#j_acb-2021-0020_ref_007">7</a>].</p>
<p>The World Health Organization (WHO) has provided new nomenclature for VOC on 31 May 2021 using Greek letters: Alpha for B.1.1.7; Beta for B.1.351; Gamma for P.1; Delta for B.1.617.2, and others. Beta variant (B.1.351 VOC-20DEC-02 (VOC-202012/02), GH/501Y.V2) of coronavirus is characterized by 17 mutations, which are: eight spike protein mutations (D80A, D215G, 241/243 deletion, K417N, E484K, N501Y, D614G, and A701V), four open reading frame 1a (orf1a) mutations, one orflb mutation, one nucleocapsid (N) protein mutation and three others [<a ref-type="bibr" href="#j_acb-2021-0020_ref_008">8</a>]. RNA-dependent RNA polymerase (RdRp) is one of the non-structural proteins (NSPs) derived from the polyprotein encoded ORF1 of SARS-CoV-2 [<a ref-type="bibr" href="#j_acb-2021-0020_ref_009">9</a>]. Non-structural protein (nsp) of SARS-CoV-2 which include 3-Chymotrypsin-like protease (3CL<sup>pro</sup>), Papain-like protease (PL<sup>pro</sup>), helicase (nsp13), RdRp (nsp12), 2’-O-ribose methyltransferase (nsp16) has been investigated computationally, as potential targets for therapeutic discovery [<a ref-type="bibr" href="#j_acb-2021-0020_ref_010">10</a>]. V843F and A889V are the two mutations reported for PLPro, with V843F mutation being the most prevalent mutation in the clinical samples [<a ref-type="bibr" href="#j_acb-2021-0020_ref_011">11</a>]. It has been reported that PLpro (PDB ID: 5Y3E) is less deformed and could be less susceptible during viral mutations [<a ref-type="bibr" href="#j_acb-2021-0020_ref_010">10</a>]. <italic>In silico</italic> approach has been used to compare annotated functional domains of SARS-CoV and SARS-CoV-2 sequences. An <italic>in silico</italic> molecular dynamics study on the protein structure was used to predict amino acid residues T478K mutation in Spike protein and that might significantly alter the electrostatic surface of the protein and their binding with human receptor angiotensin-converting enzyme 2 (ACE2) as well as prevention and curative measures such as vaccines, antiviral drugs, and monoclonal antibodies [<a ref-type="bibr" href="#j_acb-2021-0020_ref_012">12</a>]. In this study, the structural fluctuations of the amino acid residues in the spike glycoprotein and nsp12 of SARS-CoV-2 were investigated by <italic>in silico</italic> approach to decipher susceptibility to mutation.</p>
</sec>
<sec id="j_acb-2021-0020_s_002"><div>Materials and methods</div>
<sec id="j_acb-2021-0020_s_002_s_001"><div>Structure preparation</div>
<p>Briefly, From the crystal structure of Spike glycoprotein and RNA-dependent RNA polymerase (nsp12) of SARS-CoV-2 were obtained from the protein databank (<ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.rcsb.org/pdb">www.rcsb.org/pdb</ext-link>) in pdb format and they were prepared for simulation by removing all water molecules, multichain, and heteroatoms using PyMol v 2.0.7.</p>
</sec>
<sec id="j_acb-2021-0020_s_002_s_002"><div>Molecular structure dynamics simulation of normal SARS-CoV-2 proteins</div>
<p>The prepared crystal structures of Spike Glycoprotein (PDB ID: 7CAB, chain A) and RNA-dependent RNA polymerase (PDB ID: 7BW4, chain A) of SARS-CoV-2 were subjected to fast simulation of structural flexibility using CAB-flex 2.0 server [<a ref-type="bibr" href="#j_acb-2021-0020_ref_013">13</a>], all parameters were at default settings. The contact map and root-mean square fluctuations (RMSF) of atoms in the server analyzed protein was obtained.</p>
</sec>
<sec id="j_acb-2021-0020_s_002_s_003"><div>Molecular structure dynamics simulation of mutated SARS-CoV-2 proteins</div>
<p>The prepared crystal structures of Spike Glycoprotein (PDB ID: 7CAB, chain A) of SARS-CoV-2 was edited with the following mutations: <bold>T478K</bold>, <bold>E484K, N501Y, D614G, A701V</bold> and RNA-dependent RNA polymerase (PDB ID: 7BW4, chain A) of SARS-CoV-2 was edited with the following mutations: <bold>G228C, P323L, V330E, D824Y</bold> [<a ref-type="bibr" href="#j_acb-2021-0020_ref_003">3</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_008">8</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_009">9</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_014">14</a>]. These were subjected to fast simulation of structural flexibility using CAB-flex 2.0 server [<a ref-type="bibr" href="#j_acb-2021-0020_ref_013">13</a>], all parameters were at default settings. The contact map and root-mean square fluctuation (RMSF) of atoms in the server analyzed protein was obtained.</p>
</sec>
<sec id="j_acb-2021-0020_s_002_s_004"><div>Assessment of mutational effect on the SARS-CoV-2 protein</div>
<p>The structural differences between the normal and mutated proteins were estimated by model-by-model basis on the Dali Server (<ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://ekhidna2.biocenter.helsinki.fi/dali/#tabs-3">http://ekhidna2.biocenter.helsinki.fi/dali/#tabs-3</ext-link>, [<a ref-type="bibr" href="#j_acb-2021-0020_ref_015">15</a>]). The root-mean square deviations (RMSD) were obtained.</p>
</sec>
</sec>
<sec id="j_acb-2021-0020_s_003"><div>Results</div>
<p>The result of this study showed that RNA-dependent RNA polymerase (nsp12) with amino acid residues (rmsf) 40 (3.00 Å), 50 (3.79 Å), 119 (4.56 Å), 120 (3.53 Å), 220 (3.84 Å), 263 (3.33 Å), 265 (4.31 Å), 270 (3.30 Å), and 499 (3.00 Å) could be very susceptible to mutation as shown in <bold><a ref-type="fig" href="#j_acb-2021-0020_fig_001">figure 1</a></bold>. The result of this study showed that spike glycoprotein with amino acid residues (rmsf) 282 (3.65 Å), 477 (4.21 Å), 478 (4.82 Å), 479 (5.40 Å), 481 (5.94 Å), 560 (4.63 Å), 703 (3.94 Å), 704 (4.02 Å), 848 (4.58 Å), 1041 (3.94 Å), 1144 (4.56 Å) and 1147 (4.61 Å) could be very susceptible to mutation as shown in <bold><a ref-type="fig" href="#j_acb-2021-0020_fig_002">figure 2</a></bold>.</p>
<figure id="j_acb-2021-0020_fig_001" position="float" fig-type="figure"><h2>FIGURE 1</h2>
<figCaption><p>Structural dynamics of RNA-dependent RNA polymerase (PDB ID: 7BW4, chain A) and its mutant consisting of G228C, P323L, V330E, and D824Y. (A) Superimposition of 10 model structures of 7BW4 from CAB-flex 2.0 server. (B) Superimposition of 10 model structures of 7BW4 mutant from CAB-flex 2.0 server. (C) RMSF of amino acids residues in 7BW4 and 7BW4 mutant. (D) Comparison of model protein structures from Dali Server</p></figCaption>
<img xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/j_acb-2021-0020_fig_001.jpg" src="https://sciendo-parsed.s3.eu-central-1.amazonaws.com/64706dbd83f1392090d69631/j_acb-2021-0020_fig_001.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&amp;X-Amz-Date=20240520T182747Z&amp;X-Amz-SignedHeaders=host&amp;X-Amz-Expires=18000&amp;X-Amz-Credential=AKIA6AP2G7AKP25APDM2%2F20240520%2Feu-central-1%2Fs3%2Faws4_request&amp;X-Amz-Signature=34ed303e96351be65389496bb77c4397e7dc3c826af7f6cb2cb336eca5f7948f" class="mw-100"/>
</figure>
<figure id="j_acb-2021-0020_fig_002" position="float" fig-type="figure"><h2>FIGURE 2</h2>
<figCaption><p>Structural dynamics of Spike glycoprotein (PDB ID: 7CAB, chain A). and its mutant consisting of T478K, E484K, N501Y, D614G, and A701V. (A) Superimposition of 10 model structures of 7CAB from CAB-flex 2.0 server. (B) Superimposition of 10 model structures of 7CAB mutant from CAB-flex 2.0 server. (C) RMSF of amino acids residues in 7CAB and 7CAB mutant. (D) Comparison of model protein structures from Dali Server</p></figCaption>
<img xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/j_acb-2021-0020_fig_002.jpg" src="https://sciendo-parsed.s3.eu-central-1.amazonaws.com/64706dbd83f1392090d69631/j_acb-2021-0020_fig_002.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&amp;X-Amz-Date=20240520T182747Z&amp;X-Amz-SignedHeaders=host&amp;X-Amz-Expires=18000&amp;X-Amz-Credential=AKIA6AP2G7AKP25APDM2%2F20240520%2Feu-central-1%2Fs3%2Faws4_request&amp;X-Amz-Signature=d63c51a0e8965f0287bb8f450a9cf49ec972e598ef17013af20166d3da8bf0aa" class="mw-100"/>
</figure>
<p>The SAR-CoV-2 mutations destabilized the overall protein structure in multiples of amino acid residues which could interfere with active site leading to insensitivity or resistance to the inhibitors as seen in <a ref-type="fig" href="#j_acb-2021-0020_fig_001">Figure 1C</a> and <a ref-type="fig" href="#j_acb-2021-0020_fig_002">2C</a>. Mutation T478K of Spike glycoprotein showed the highest deviation in the structure while other mutations seem to limitedly affected the structure.</p>
</sec>
<sec id="j_acb-2021-0020_s_004"><div>Discussion</div>
<p>The results of comparison of protein sequences SARS-CoV-2 and SARS-CoV by Blastp, has shown that orf8 and orf10 proteins were not present in SARS-CoV, while surface glycoprotein, nsp2, nsp3, orf3a, and orf6 proteins, have percent identity of less than 80% of variation between SARS-CoV-2 and SARS-CoV [<a ref-type="bibr" href="#j_acb-2021-0020_ref_016">16</a>]. According to the alignment analysis, the closest similarity was between the two COVID-19 genomes (99%) compared with the two bat CoV [<a ref-type="bibr" href="#j_acb-2021-0020_ref_004">4</a>]. The orf1a polyprotein of SARS-CoV-2 is similar to that SARS-CoV by 80.58% identity [<a ref-type="bibr" href="#j_acb-2021-0020_ref_016">16</a>]. Spike glycoprotein Receptor-Binding Domain (RBD; aa 319-541), has vital functional and antigenic properties, and any mutation in this region has potential for reduced susceptibility to neutralizing antibodies elicited by vaccination or prior infection [<a ref-type="bibr" href="#j_acb-2021-0020_ref_017">17</a>].</p>
<p>D614G mutation in spike glycoprotein and P323L in RNA-dependent RNA polymerase (nsp12) are the globally dominant variants with a high frequency [<a ref-type="bibr" href="#j_acb-2021-0020_ref_014">14</a>]. Variant of Nextstrain cluster 20A.EU2 has been reported with mutation of S477N in spike protein of the new SARS-CoV-2, which was rapidly increased in France at the start of the second wave, probably due to initiation effects, and prevalent also in Belgium, Czech, Denmark, Hungary, Netherlands, and Switzerland [<a ref-type="bibr" href="#j_acb-2021-0020_ref_018">18</a>]. The P681H mutation is also characteristic of the new SARS-CoV-2 variants from the United Kingdom and Nigeria [<a ref-type="bibr" href="#j_acb-2021-0020_ref_003">3</a>].</p>
<p>A recent report on the distribution of the Spike mutation S:T478K and its recent growth in prevalence in the SARS-CoV-2 population of Mexico, United States, and several European countries, showed that S:T478K is frequently co-occurring with three other Spike mutations; D614G, P681H and T732A, with 99.83%, 93.8% and 88.7% co-occurrence respectively as well as two amino acid residues mutation in Nucleocapsid (N:RG203KR), and mutations in nsp12 [<a ref-type="bibr" href="#j_acb-2021-0020_ref_009">9</a>]. Moreover, bioinformatics study has predicted G476S, and T478I mutation in spike glycoprotein and G25Y, G228C, V330E, L810H and D824Y in nsp12 [<a ref-type="bibr" href="#j_acb-2021-0020_ref_014">14</a>]. A study has reported that mutations in 2891, 3036, 14408, 23403 and 28881 positions of SARS-CoV-2 genomic sequence, are predominantly observed in Europe, whereas those located at positions 17746, 17857 and 18060 are exclusively present in North America [<a ref-type="bibr" href="#j_acb-2021-0020_ref_019">19</a>]. These mutations were belonged to the sequence of ORF1ab (1397 nsp2, 2891 nsp3, 14408 nsp12 (RdRp), 17746 and 17857 nsp143, 18060 nsp14), S (23403, spike protein) and ORF9a (28881, nucleocapsid phosphoprotein), respectively [<a ref-type="bibr" href="#j_acb-2021-0020_ref_019">19</a>]. Interestingly, the docking site for inhibitors is not within the catalytic domain of the RdRp [<a ref-type="bibr" href="#j_acb-2021-0020_ref_010">10</a>] but the docking site for inhibitors of the spike glycoprotein is on the Receptor-Binding Domain in the N-terminal region of S1 which is responsible for viral attachment to target cells via the ACE2 receptor [<a ref-type="bibr" href="#j_acb-2021-0020_ref_017">17</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_020">20</a>].</p>
<p>The VOC B.1.1.529 (Omicron) belongs to Pango lineage B.1.1.529, Nextstrain clade 21K, is the most divergent variant, and characterized by 30 amino acid substitutions, 3 deletions and one insertion in the spike protein compared to the original virus (A67V, del69-70, T95I, del142-144, Y145D, del211, L212I, ins214EPE, G339D, S371L, S373P, S375F, K417N, N440K, G446S, S477N, T478K, E484A, Q493R, G496S, Q498R, N501Y, Y505H, T547K, D614G, H655Y, N679K, P681H, N764K, D796Y, N856K, Q954H, N969K, L981F) [<a ref-type="bibr" href="#j_acb-2021-0020_ref_021">21</a>]. Most of the substitutions in the sequence coding the spike protein have been found associated with almost complete escape from neutralization by convalescent and vaccinee sera [<a ref-type="bibr" href="#j_acb-2021-0020_ref_022">22</a>].</p>
</sec>
<sec id="j_acb-2021-0020_s_005"><div>Conclusions</div>
<p>This study has shown key amino acid residues of SARS-CoV-2 spike glycoprotein and nsp12 that could be susceptibility to mutation. Overall, spike glycoprotein has highest number of mutations and these variants could increase the risk to human health if not mitigated in the population. Consequently, it is imperative to investigate and characterize SARS-CoV-2 spike glycoprotein and nsp12 (RdRp) mutation in order to assess possible drug-resistance viral phenotypes. However, based on the existing classification, these variants may not be of interest or high consequence, in that currently no coherent proof that efficacy of prevention and curative measures such as vaccines, antiviral drugs, and monoclonal antibodies, are significantly decreased in comparison to earlier perpetrating variants [<a ref-type="bibr" href="#j_acb-2021-0020_ref_021">21</a>,<a ref-type="bibr" href="#j_acb-2021-0020_ref_023">23</a>]. As of 1 December 2021, a total of 7,885,790,810 vaccine doses have been administered globally [<a ref-type="bibr" href="#j_acb-2021-0020_ref_001">1</a>]. Thus, there should be concerted efforts toward administration and development of holistic vaccines that will directly target the existing and emergent variants of SARS-CoV-2.</p>
</sec>
</div>

Susceptibility of spike glycoprotein and RNA-dependent RNA polymerase of SARS-CoV-2 to mutation: in silico structural dynamics study

Medical Journal of Cell Biology

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a microorganism that causes coronavirus disease 2019 (COVID-19). Mutations affect...

Susceptibility of spike glycoprotein and RNA-dependent RNA polymerase of SARS-CoV-2 to mutation: in silico structural dynamics study

Published Online: Dec 30, 2021

Page range: 148 - 152

Received: Oct 02, 2021

Accepted: Nov 18, 2021

DOI: https://doi.org/10.2478/acb-2021-0020

Keywords
SARS-CoV-2, omicron variant, spike glycoprotein, RNA-dependent RNA polymerase, mutation, structural analysis

© 2021 Toluwase Hezekiah Fatoki et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

FIGURE 1

FIGURE 2

Susceptibility of spike glycoprotein and RNA-dependent RNA polymerase of SARS-CoV-2 to mutation: in silico structural dynamics study

Published Online: Dec 30, 2021

Page range: 148 - 152

Received: Oct 02, 2021

Accepted: Nov 18, 2021

DOI: https://doi.org/10.2478/acb-2021-0020

KeywordsSARS-CoV-2, omicron variant, spike glycoprotein, RNA-dependent RNA polymerase, mutation, structural analysis

© 2021 Toluwase Hezekiah Fatoki et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

FIGURE 1

FIGURE 2

Keywords
SARS-CoV-2, omicron variant, spike glycoprotein, RNA-dependent RNA polymerase, mutation, structural analysis